One can summon up the problem of Cutthroat Island with one word: The script. Multiple writers were working on this one, it was rewritten while the filming was still going on, and it shows. For example, in one scene it is revealed the Morgan Adams can't read, in another she suddenly realizes that the words are not Latin at all. (If you have the option, try a different dubbing...I noticed that the dialogues in the German dubbing are way snappier and more to the point).
But if you are able to overlook the battling storylines and are just into it for what most people like about Pirate movies, meaning some adventure, good fight scenes and a lot of fun, the movie delivers in every sense of the word. A hidden treasure, a ship wreck, a lot of battles and a lot of explosions making this one a fun watch. It also gets bonus points for turning the tables and having for once a female action hero (with some really well done stunt-scenes)and a dude-in-distress. And naturally for the outstanding soundtrack.
All in all certainly worth at least one watch. It might not be a masterpiece, but its good entertainment nevertheless.